# US 2014/0151941 A1 · Hood-type annealing furnace and method for operating the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0151941 A1 - Document ID: US20140151941A1 - Status: Published application - Kind: A1 - Application number: 14/093,847 - Filed: 2013-12-02 - Published: 2014-06-05 - Earliest claimed: 2012-11-30 - Assignees: Bilstein GmbH & Co.KG - Applicants: Bilstein GmbH & Co. KG - Inventors: GERALD ZWICKEL - Web page: https://patentgrep.com/patent/US20140151941A1 ## CPC - F27D 7/06: Forming or maintaining special atmospheres or vacuum within heating chambers (supplying steam, vapour, gases or liquids F27D7/02) - C21D 9/677: Arrangements of heating devices - F27B 11/00: Bell-type furnaces - F27D 7/02: Supplying steam, vapour, gases or liquids - F27D 7/04: Circulating atmospheres by mechanical means - F27D 99/0006: {Electric heating elements or system} - F27D 99/0033: {using burners} - F27D: DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE - C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B) - F27B: FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS ## Abstract A hood-type annealing furnace for the thermal treatment of cold-rolled steel strip includes a base, a protective hood which can be placed on the latter and under which a protective gas heated by a gas burner is circulated by a blower, to heat the steel strip, rolled up particularly into a coil, under the protective hood to a temperature of at least 500° C. in a protective gas atmosphere. An electric heater fed by the public power network has a heating capacity correspondingly substantially to the heating capacity of the gas burner. The protective gas can be independently heated with the electric heater, alternatively to the gas burner, with the gas burner switched off, to a temperature above the recrystallization annealing temperature. A method for operating a hood-type annealing furnace is also provided. ## Claims ### Claim 1 A hood-type annealing furnace for the thermal treatment of cold-rolled steel strip, the hood-type annealing furnace comprising: a base; a protective hood configured to be placed on said base and to receive the steel strip under said protective hood; a gas burner having a heating capacity and being configured to heat a protective gas atmosphere; a blower configured to circulate the protective gas atmosphere heated by said gas burner under said protective hood and to heat the steel strip under said protective hood to a temperature of at least 500° C. in the protective gas atmosphere; and an electric heater fed by a public power network and having a heating capacity corresponding substantially to said heating capacity of said gas burner, said electric heater configured to independently heat the protective gas atmosphere as an alternative to said gas burner to a temperature above a recrystallization annealing temperature with said gas burner switched off. ### Claim 2 (depends on 1) The hood-type annealing furnace according to claim 1, wherein the steel strip is rolled up into a coil. ### Claim 3 (depends on 1) The hood-type annealing furnace according to claim 1, which further comprises a controller configured to interrupt a supply of gas to said gas burner and activate said electric heater in the event of a surplus of electrical energy in the public power network. ### Claim 4 (depends on 3) The hood-type annealing furnace according to claim 3, wherein said electric heater includes a multiplicity of individual low-power electric heaters, and said controller is configured to electrically connect said low-power electric heaters to the public power network in succession individually or in groups, upon said hood-type annealing furnace being switched over to electrical heating operation. ### Claim 5 (depends on 1) The hood-type annealing furnace according to claim 1, which further comprises: a heating hood surrounding said protective hood and defining a combustion space between said protective hood and said heating hood; said combustion space configured to contain a flame and hot exhaust gas of said gas burner acting with thermal energy upon an outside of said protective hood; and said electric heater being accommodated at least one of outside a stream of the exhaust gas below said gas burner or in a portion of said heating hood set back radially with respect to said combustion space. ### Claim 6 (depends on 4) The hood-type annealing furnace according to claim 4, wherein said protective hood has an inner space, and said electric heater is configured to act with thermal energy upon an outside said protective hood to indirectly heat the protective gas atmosphere circulating in said inner space, through a wall of said protective hood. ### Claim 7 (depends on 4) The hood-type annealing furnace according to claim 4, wherein said low-power electric heaters include a multiplicity of NIR emitters configured to act directly with infrared radiation upon an outside of said protective hood. ### Claim 8 (depends on 5) The hood-type annealing furnace according to claim 5, wherein said electric heater includes a multiplicity of NIR emitters configured to act directly with infrared radiation upon an outside of said protective hood. ### Claim 9 (depends on 1) The hood-type annealing furnace according to claim 1, which further comprises a closed circuit including a heat exchanger disposed outside said protective hood and a further blower configured to circulate the protective gas atmosphere through said heat exchanger, said electric heater configured to act with thermal energy upon said heat exchanger from outside to heat the protective gas atmosphere circulated through said heat exchanger. ### Claim 10 (depends on 9) The hood-type annealing furnace according to claim 9, wherein said electric heater includes a multiplicity of NIR emitters disposed inside said heat exchanger and being washed around by the circulating protective gas atmosphere. ### Claim 11 (depends on 10) The hood-type annealing furnace according to claim 10, wherein said heat exchanger has an inner space and a sheet-shaped component disposed in said inner space and configured to have the protective gas atmosphere flow around said sheet-shaped component, and said multiplicity of NIR emitters inside said heat exchanger are configured to act directly with infrared radiation upon said sheet-like component. ### Claim 12 (depends on 11) The hood-type annealing furnace according to claim 11, wherein said sheet-like component is a metal sheet. ### Claim 13 (depends on 1) The hood-type annealing furnace according to claim 1, wherein said electric heater and said gas burner are configured to be operated simultaneously to shorten a heating phase of the hood-type annealing furnace. ### Claim 14 A method for operating a hood-type annealing furnace for the thermal treatment of cold-rolled steel strip, the method comprising the following steps: providing a hood-type annealing furnace including: a base, a protective hood configured to be placed on the base and to receive the steel strip under the protective hood, a gas burner having a heating capacity and being configured to heat a protective gas atmosphere, a blower configured to circulate the protective gas atmosphere heated by the gas burner under the protective hood and to heat the steel strip under the protective hood to a temperature of at least 500° C. in the protective gas atmosphere, and an electric heater fed by a public power network and having a heating capacity corresponding substantially to the heating capacity of the gas burner, the electric heater configured to independently heat the protective gas atmosphere as an alternative to the gas burner to a temperature above a recrystallization annealing temperature with the gas burner switched off; upon a surplus of electrical energy occurring in the public power network, connecting the electric heater to the public power network using a controller until the coils have assumed the recrystallization annealing temperature or a stipulated maximum temperature lying above the recrystallization annealing temperature; and subsequently breaking the electrical connection between the electric heater and the public power network using the control device and making at least one further electrical connection to an electric heater of at least one substantially identically constructed further hood-type annealing furnace, until reaching a reduction in the surplus of electrical energy in the public power network.